Secretory cells from rat pituitaries are studied in vitro to compare their physiology in old and yound animals. Production of TSH and prolactin in response to TRH and production of LH and FSH and their subunits in response to LRH are being measured in order to investigate altered function of pituitary secretory cells. Deranged function of aged pituitary cells in vitro has been found. Castration increases LRH responsiveness of gonadotrophs of aged and young rats to the same extent. Pretreatment of rats with LRH has partially restored LH secretory function of cells from old animals, suggesting that hypothalamic deficiency is, at least in part, responsible for the observed age-related reduction in LH secretion.